1. Field of the Description
The present invention relates, in general, to autostereoscopic displays, to holography and to holographic displays, and, more particularly, to displays adapted to utilize optical vortices to create three dimensional (3D) displays.
2. Relevant Background
Recently, the demand for 3D displays has rapidly expanded both for theater and similar settings for larger audiences and for smaller applications, such as for home theaters and televisions, with a smaller number of viewers. One approach to providing 3D displays is labeled or named “multi-view 3D displays.” In these displays, a set of two dimensional (2D) images is directed into different view zones, which provides different views for each eye at different locations. Multi-view 3D displays are desirable in part because the different views for each eye provide multiple stereo views and 3D parallax. Another approach is the use of so called multi-planar 3D displays. In these displays, a set of 2D images are directed onto different depth layers. Multi-planar 3D displays are desirable in part because they provide 3D depth, parallax, and accommodation cues.
One challenge facing designers and manufacturers of multi-view/multi-planar 3D displays is the mechanism or technique of distributing the 2D images into the different view zones (e.g., into different viewers' eyes) or onto different depths. All eyes or viewers' eyes are essentially identical except for their placement in a view zone (e.g., all are spaced apart about 2.5 inches), and, similarly, projection screens that can be placed apart at different depths in a multi-view 3D display are typically made of the same material. Light intended for different eyes or different screen layers must be accurately and precisely directed only where it is intended for a multi-view/multi-planar 3D display to properly function. This may involve use of temporal multiplexing, directional backlights, spatially multiplexed parallax barriers/lenticulars, and the like. Alternatively, some device has to be utilized to help the eyes and screens discriminate between light intended for them (the eyes or screens) and light intended for others (other eyes or other screens), and such discrimination may be performed using light wavelengths, polarization of the light (e.g., with a viewer wearing special 3D glasses), or synchronized shuttering between an image source and viewers' eyes or a screen.
To better understand challenges of providing 3D displays, it may be informative to examine a related analogy with 3D stereo with colored or polarized glasses. Colored glasses (e.g., anaglyph glasses) and polarized glasses are common devices that are used to help a viewer's eye to discriminate between light intended for that particular eye and light intended for another eye (e.g., for their other eye). In 3D viewing with colored glasses, left and right images are encoded using chromatically opposite colors such as red and cyan, and the glasses have matching colored filters positioned over each of the wearing viewer's eyes. The viewer's brain acts to merge the two different colored images into a single full color image, but sometimes this can result in binocular color rivalry and eye strain. Some glass technologies use two slightly different wavelengths for red, green, and blue for each eye, as the eye is not sensitive to slight color differences. The left and right eyes of the viewer see images of similar color and brightness, which relieves retinal rivalry. However, these glasses are expensive to fabricate as the filters have to be extremely selective to wavelengths that are very close to each other. A further limit of wavelength-based 3D glasses is that some designs only use two sets of wavelengths, which limits their use to two or stereo views.
Polarized glasses similarly help discriminate between views intended for the viewer's left and right eyes. In these 3D systems, left-right images are encoded using oppositely oriented polarized light, and the viewers each wear glasses with matching polarization filters over each eye. The human eye is largely insensitive to polarization so that each eye of a viewer wearing polarized glasses sees images of similar color and brightness. Polarized light is a combination of two polarization directions, e.g., horizontal and vertical. As a result, a limit with the use of polarized light is that a 3D display system designer can only encode two views using only polarization (as is the case with some wavelength-based 3D display systems).
Display systems using color/wavelength and polarized encoding project onto screens. Each screen, being projected upon, sends the encoded light into all directions, and transmission filters placed (by 3D glasses) over each eye act to select the appropriate image for that particular eye. Again, only two polarizations or two sets of wavelengths are needed to discriminate between a viewer's left and right eyes. Such an arrangement is adequate for use in a cinema setting where each viewer does not change their viewpoint. However, for multi-view autostereo displays (i.e., displays where viewers do not wear special eyewear), more than two images must be encoded, and a screen would need to reflect (or bend) light into a different direction based upon the wavelength or polarization. Layer discrimination is also problematic in this regard because it would require a color/wavelength or polarization-selective scattering/transparent screen.